Two-cycle engine with exhaust temperature-controlled ignition timing

ABSTRACT

A two-cycle internal combustion engine has an ignition timing that varies with engine speed. A plurality of ignition patterns (the relationship between ignition timing and engine speed) are used. The engine exhaust gas temperature is sensed and is used to determine the particular ignition pattern used at a particular time.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 09/568,449,filed May 10, 2000, now U.S. Pat. No. 6,371,082, which is acontinuation-in-part of Ser. No. 09/452,657, filed Dec. 1, 1999, nowU.S. Pat. No. 6,237,566, which application(s) are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention is directed to a two-cycle internal combustionengine and the operation of such an engine. Such engines are used, forexample, to drive various vehicles such as snowmobiles, motorcycles,personal watercraft and others.

The operation of such engines is based on the ignition of a compressedfuel-air mixture within a cylinder, with the resulting expansion of theignited mixture driving a reciprocating piston located in the cylinder.The reciprocating movement of the piston then is used to drive thevehicle powered by the engine.

It is desirable to vary the point during the reciprocation cycle of thepiston at which the fuel-air mixture is ignited, i.e. a point between“bottom dead center” and “top dead center”, to provide optimum operationof the engine. Thus, as one example the optimum point of ignition duringacceleration can differ from that for a normal running operation.Because the piston usually is driven by a rotating crank shaft, theignition point often is expressed in terms of degrees of advancementwith respect to top dead center, in other words the position withrespect to degrees of rotation of the rotating crank shaft ahead of thetop dead center position.

Typically, different engine operating speeds, which usually areexpressed in revolutions per minute, will be associated with differentengine conditions. For example, higher engine speeds often areassociated with acceleration. Thus, it has been considered that thepoint of ignition during the reciprocation cycle of the piston should bevaried, depending on the engine operating speed at the particular time,and engine ignition control systems can be programmed to vary theignition point depending on the engine speed.

Other factors can affect the optimum ignition timing. For example, anengine operating shortly after start-up may require a differentrelationship between ignition timing and engine speed (hereinafter“ignition pattern”) than an engine that has been operating from sometime. Consideration has been given in the past to a system that allowsthe user to switch between two different ignition patterns. This has notbeen completely satisfactory in optimizing engine performance.

SUMMARY OF THE INVENTION

The present invention seeks to provide a two-cycle engine that enjoysimproved performance by selecting from a plurality of relationshipsbetween ignition timing and engine speed (ignition patterns) based onexhaust gas temperature. In one aspect of the present invention,individual ignition patterns cover ranges of exhaust gas temperature ofabout 50 C. The sensitivity of the control system increases as thetemperature range decreases. In another aspect of the present inventionthe exhaust gas temperature is determined by use of a sensor that is incontact with the exhaust gas, for example in an exhaust pipe. In afurther aspect of the invention, a capacitor discharge ignition systemis used to control the ignition timing of a spark plug. Yet anotheraspect of the invention provides for a default ignition pattern whenthere is a malfunction of the temperature sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an example of an engine inaccordance with the present invention.

FIGS. 2 and 3 are flow charts illustrating examples of the control ofthe ignition timing.

FIGS. 4-8 are graphs illustrating examples of different ignitionpatterns that can be used in the present invention.

DETAILED DESCRIPTION

The present invention will be described with reference to theaccompanying drawings. It should be understood that the presentinvention is not limited to the specific embodiments of this descriptionand the drawings.

Referring to FIG. 1, a two cycle engine 10 includes a cylinder 12 andpiston 14 that moves reciprocally within the cylinder. The movement ofthe piston 14 may be controlled with a crank shaft 16. Fuel-air mixtureintroduced into the cylinder is compressed during the upward movement ofthe piston with in the cylinder and is ignited by an ignition source 18,for example a spark plug. The expansion resulting from the resultingcombustion drives the piston downward, thereby imparting rotation to thecrank shaft, which in turn can be used to drive a vehicle on which theengine is mounted. Examples of vehicles that typically make use of suchtwo cycle engines include snowmobiles, personal watercraft, motorcyclesand the like, although the present invention is not limited thereto. Inaddition, the present invention could be applied to two cycle enginesused in a stationary setting if desired. Exhaust gas resulting from thecombustion of the fuel-air mixture is expelled from the cylinder, forexample through an exhaust pipe 28. The present invention is not limitedto any particular exhaust system, and various combinations of exhaustpipes and manifolds can be used with engines that have more than onecylinder.

Controller 20 is provided for controlling the ignition of the ignitionsource 18. In one embodiment, the controller is a capacitor dischargeignition system, and activates a spark plug through coil 22. However,other ignition and control systems can be used as well, such aselectronic ignition systems. Generally, the ignition should take placewhile the piston is moving upwardly, i.e. during the compressionmovement by the piston. Typically the ignition takes place shortlybefore the piston reaches the end of the compression movement (the “topdead center” position). The ignition timing can be expressed withrespect to the rotation of the crank shaft, i.e. in terms of a certainnumber of degrees before the top dead center position.

Different effects of the combustion can be achieved by varying theignition timing. Thus, depending on the desired affect, in some cases itis desirable to have an earlier or “advanced” ignition. Thecircumstances in which particular effects are desired can be correlatedto engine speed. Thus, at a particular engine speed a particularadvancing of the ignition timing will be used. In some ignition systems,the ignition timing is based only on engine speed (so-called2-dimensional ignition systems). In other ignition systems, timing isbased on engine speed and throttle position (so-called 3-dimensionalignition systems). Both are applicable to the present invention. In anycase, the various combinations of ignition timings and particular enginespeeds thus will form a particular ignition pattern.

Different engine operating conditions may result in different ignitionpatterns being desirable. That is, in one circumstance one particularignition pattern may be the most useful, while another pattern might bebetter under different conditions. In accordance with the presentinvention, the exhaust gas temperature is used to evaluate operatingconditions and thus determine which of two or more ignition patternsshould be selected for engine operation. For this purpose, an exhaustgas temperature sensor 24 is provided. It is preferred that the sensor24 be in direct contact with the exhaust gas for the purposes ofaccuracy and reduction in reaction time, for example by being positionedin the exhaust pipe 26. However, it is possible to sense the temperatureon the outside of part of the exhaust system or to sense the temperatureof water in a water jacket surrounding an exhaust pipe. In the case of asensor directly contacting exhaust gas in the exhaust pipe or other partof the exhaust system, the sensor should be able to withstand thatenvironment, and suitable measures should be taken to seal the exhaustsystem at the point where the sensor extends into the exhaust system. Anexample of a suitable sensor for use in directly contacting the exhaustgas is a thermistor. It is desirable that the sensor be positioned inthe exhaust system at a position sufficiently far from the engine toavoid sharp rises and falls (spikes) in temperature of short duration.However, if the sensor is too far from the engine the responsiveness ofthe system is adversely affected, i.e. there will be too much delay insensing increases and decreases in temperature. The exact position isdetermined based on the specific characteristics of the exhaust systeminvolved.

The sensor 24 provides information concerning the exhaust gastemperature to the controller 20. For example, in the case where athermistor is used as the sensor, the sensor sends an electrical signalwhose magnitude changes with changes in the exhaust gas temperature. Thecontroller then selects an ignition pattern based on the exhaust gastemperature information. The selected ignition pattern then is used tocontrol the ignition advance based on the engine operating speed. Inthis regard, a signal can be sent from the crank shaft to the controllerto indicate the engine speed and the relative position of the crankshaft so that the desired ignition timing can be provided.

The controller can process the temperature information as desired. Forexample, in one embodiment the controller can take the average ofseveral readings, e.g. 10, with the readings being taken by the sensorevery 2 milliseconds as one example. Other methods for handling thesensor information can be used as well.

It is desirable to have a plurality of ignition patterns, each of whichcovers a particular temperature range. As one example, five patternscould be provided, each of which covers a range of about 50 C., forexample from 250 C. and lower, 250-300 C., 300-350 C., 350-400 C., 400C.+ respectively. Different numbers of patterns and differentcombinations of ranges can be used as desired for a particular practicalapplication, and it is possible to have the different patterns in asingle application cover larger and smaller temperature ranges as neededfor that particular engine.

A default ignition pattern can be provided for cases where there is afailure in the temperature sensor. Sensor failure can be determined, forexample, by the sensor reading temperatures outside expected parameters,e.g. reading above or below certain limits. Thus, as one example, atemperature reading higher than the upper sensor fail limit would beinterpreted as a short in a thermistor sensor, while a reading below thelower sensor fail limit would be interpreted as a break in the wiring ina thermistor sensor. It also is possible to allow for user selection ofignition patterns in the event of sensor failure.

It also is possible to use the sensed temperature readings to modify aparticular timing pattern that can be selected from a plurality ofpatterns. For example, the user may be able to select a timing patternfrom a plurality of timing patterns using a switch or the like, and thesensed temperatures readings can be used to modify the selected patternappropriately.

Further, in some cases the desired engine timing pattern may depend onthe type of fuel being used in the engine. In such cases, the sensedexhaust temperature may be indicative of the type of fuel and can beused to set the ignition timing pattern accordingly. Thus, the sensedtemperature can compensate for the type of fuel used, or can be used toselect a timing pattern that would avoid damage to the engine if thefuel selected is not desirable for the engine.

The sensed exhaust temperature also may be useful in indicating someproblem in engine performance, e.g. incorrect carburetion or fueldelivery. Again, in this case the sensed temperature can be used toselect a timing pattern that avoids damage to the engine.

An example illustrating the control of the ignition timing will bediscussed with respect to FIGS. 2-8. In this embodiment, a thermistortype sensor is used. FIG. 2 illustrates the control from the enginestart time. At the time the engine is started, the temperature sensor isreset. The controller then determines whether the temperatureinformation is lower than the upper sensor fail limit temperature, e.g.600 C. as one example in a case of an engine for a snowmobile. If not,the controller considers that the sensor is shorted out and switches toa “hold pattern”, which operates as a default pattern. Any of theavailable ignition patterns can be used for the default pattern, or theuser can be permitted to select one of the available patterns, or aspecial pattern can be used. If the temperature is below the uppersensor fail limit, the controller continues and determines whether theengine has been running for a sufficiently long period before the failcontrol is initiated (fail control delay time). Essentially, thispermits the engine to run for a period during which the exhaust gastemperature would be expected to exceed the lower sensor fail limittemperature. Until this period is passed, the controller checks onlywhether the sensor is reading a temperature below the upper sensor faillimit, and if not the “hold pattern” is invoked. The delay period willdepend on the lower temperature limit of the sensor, and in the case ofa sensor having a lower limit of about 200 C. the delay period generallywill be around 10-2500 seconds, with a delay of 120 seconds beingtypical.

Once the fail control delay time is passed, a further short delay timecan be invoked, e.g. on the order of five seconds. This permits the useof a different default pattern during this period under certaincircumstances. If the sensor reading is above upper sensor fail limit,the “hold pattern” is invoked. If the sensor reading is below the lowersensor fail limit an “information pattern” can be invoked, which can bethe same as or different from the “hold pattern”. The informationpattern can be such that the pattern would warn the user of sensorfailure if a failure indicator light is not provided. An example of alower sensor fail limit is 225 C. for a thermistor sensor used in a twocycle snowmobile engine. If the sensor reading is between the upper andlower sensor fail limits, a “normal” pattern is selected. The furtherdelay period should be sufficient for the controller to check for sensorfailure, for example about 5 seconds or so.

Once the further delay has passed, and assuming the “hold pattern” hasnot been invoked, the sensory memory function is activated (if sensoroutput information is to be based on averaged values of previousreadings) and normal control is invoked. Referring to FIG. 3, if the“information pattern” was invoked during the further delay, this patterncontinues until the exhaust temperature is between the upper and lowersensor fail limits. If the “information pattern” was not invoked duringthe further delay, i.e. one of the normal patterns was selected, theexhaust temperature is checked to determine whether it is between theupper and lower sensor fail limits. If so, the selection of one of thenormal patterns continues. If not, the “hold pattern” is invoked, afterwhich the system can recheck itself to determine whether there has beensensor failure (Start Memory Sensor).

The graphs of FIGS. 4-8 show amount of ignition advance (in degreesbefore top dead center) as the ordinate versus engine speed (rpm) as theabscissa for five different temperature ranges for a two cyclesnowmobile engine. The Figures represent the ignition patterns for 250C. and lower, 250-300 C., 300-350 C., 350-400 C. and 400 C.+respectively.

A further example of data that can be used to generate curves of thetype shown in FIGS. 4-8 is presented below. In these data, the “angle”represents the number of degrees before top dead center.

A. Exhaust Temperature 250C or less RPM ANGLE 8800 7.0 8600 7.0 8400 7.08200 8.0 8000 10.0 7750 12.5 7500 14.5 7250 16.0 7000 17.5 6500 20.06000 24.0 5000 24.0 4000 20.0 3000 10.0 2000 10.0 1000 8.0 0000 8.0

B. Exhaust Temperature 250-300C RPM ANGLE 8800 11.0 8600 10.0 8400 7.08200 8.0 8000 10.5 7750 13.5 7500 16.0 7250 18.0 7000 19.0 6500 22.06000 24.0 5000 24.0 4000 20.0 3000 10.0 2000 10.0 1000 8.0 0000 8.0

C. Exhaust Temperature 300-350C RPM ANGLE 8800 8.0 8600 8.0 8400 8.08200 9.0 8000 13.0 7750 15.0 7500 17.0 7250 19.0 7000 20.0 6500 22.06000 24.0 5000 24.0 4000 20.0 3000 10.0 2000 10.0 1000 8.0 0000 8.0

D. Exhaust Temperature 350-400C RPM ANGLE 8800 10.0 8600 11.0 8400 11.08200 12.0 8000 14.0 7750 15.5 7500 18.5 7250 20.0 7000 21.0 6500 22.06000 24.0 5000 24.0 4000 20.0 3000 10.0 2000 10.0 1000 8.0 0000 8.0

E. Exhaust Temperature 400C or higher RPM ANGLE 8800 11.0 8600 11.0 840011.0 8200 11.5 8000 13.0 7750 15.0 7500 18.0 7250 19.0 7000 20.0 650022.0 6000 24.0 5000 24.0 4000 20.0 3000 10.0 2000 10.0 1000 8.0 0000 8.0

The present invention has been discussed with respect to a reciprocatingpiston engine. The selection of different ignition patterns based onexhaust temperature also is applicable to other types of internalcombustion engines, such as rotary engines.

While a detailed discussion of the present invention has been providedabove, this should be considered as illustrative and not limiting. Thepresent invention is not limited to the specific embodiments describedherein but rather is defined by the following claims.

What is claimed is:
 1. A two-cycle engine, comprising; a cylinder; a piston movable in the cylinder, for compressing a fuel-air mixture to be ignited in the cylinder, with exhaust gas from combustion of the fuel-air mixture being expelled from the cylinder; an ignition source in the cylinder; a controller for activating the ignition source at a particular point during the movement of the piston, the controller containing a plurality of ignition patterns, each of said patterns reflecting desired ignition points that vary as a function of the operation speed of the engine; and a sensor for sensing a temperature of exhaust gas from the cylinder and for providing a signal to the controller indicative of the temperature of the exhaust gas; wherein the controller selects an ignition pattern based upon the sensed exhaust gas temperature.
 2. The two-cycle engine as claimed in claim 1, wherein the controller activates the ignition source during the compression movement of the cylinder.
 3. The two cycle engine as claimed in claim 2, wherein each of the ignition patterns reflects a desired ignition points at various degrees before a top dead center of the piston.
 4. The engine as claimed in claim 1, wherein the ignition source is a spark plug and the controller comprises a capacitor discharge ignition system.
 5. The engine as claimed in claim 1, wherein the sensor contacts the exhaust gas.
 6. The engine as claimed in claim 1, wherein the plurality of different ignition patterns includes a default pattern that is used if a failure of the sensor is determined.
 7. The engine as claimed in claim 1, wherein the engine is a snowmobile engine.
 8. The engine as claimed in claim 1, wherein the plurality of ignition patterns have different relationships between ignition point and engine speed.
 9. A method of operating a two-cycle engine, comprising: moving a piston in a cylinder to compress a fuel-air mixture in the cylinder; activating an ignition source in the cylinder during the movement of the piston; expelling exhaust gas from combustion of the fuel-air mixture from the cylinder; sensing a temperature of the exhaust gas expelled from the cylinder; and selecting an ignition pattern from a plurality of ignition patterns based on the sensed exhaust temperature, each of said ignition patterns reflecting desired ignition points that vary as a function of the operation speed of the engine; and controlling the activation of the ignition source according to the selected ignition pattern.
 10. The method as claimed in claim 9, wherein the activating step occurs during the compression movement of the cylinder.
 11. The method as claimed in claim 10, wherein each of the ignition patterns reflects a desired ignition points at various degress before a top dead center of the piston.
 12. The method as claimed in claim 9, wherein the ignition spark is a spark plug and the controlling step is performed by a capacitor discharge ignition system.
 13. The method as claimed in claim 9, wherein the sensing step is performed by a sensor that contacts the exhaust gas.
 14. The method as claimed in claim 9, wherein the temperature of the exhaust gas is sensed with a temperature sensor and the plurality of different ignition patterns includes a default pattern that is selected when a failure of the temperature sensor is determined.
 15. The method as claimed in claim 9, wherein the engine is a snowmobile engine.
 16. The method as claimed in claim 9, wherein the plurality of ignition patterns have different relationships between ignition point and engine speed.
 17. A method of operating a two-cycle engine having a piston movable within a cylinder, an ignition source to ignite fuel in the cylinder, an exhaust system for carrying exhaust gas expelled from the cylinder, and a controller for controlling activation of the ignition source, the method comprising: storing a plurality of ignition patterns in the controller, each of said ignition patterns reflecting desired ignition points that vary as a function of the operation speed of the engine at a particular range of exhaust gas temperatures; moving the piston in the cylinder to compress a fuel-air mixture in the cylinder; activating the ignition source in the cylinder during the compression movement of the piston; expelling exhaust gas from the cylinder; sensing a temperature of the exhaust gas expelled from the cylinder; and selecting a desired ignition pattern based on the sensed exhaust gas temperature; and controlling the activation of the ignition source according to the selected ignition pattern.
 18. The method as claimed in claim 17, wherein each of the ignition patterns reflects a desired ignition points at various degrees before top dead center of the piston.
 19. The method as claimed in claim 17, wherein the sensing step is performed by a sensor that contacts the exhaust gas.
 20. The method as claimed in claim 17, wherein the temperature of the exhaust gas is sensed with a temperature sensor and the plurality of different ignition patterns includes a default pattern that is selected when a failure of the temperature sensor is determined.
 21. The method as claimed in claim 17, wherein the plurality of ignition patterns have different relationships between ignition point and engine speed. 